Siemens Healthcare Diagnostics, part of Siemens (NYSE:SI), has received a warning letter from the U.S. Food and Drug Administration over allegedly changing without following proper protocol the design of an immunoassay device used to test blood and other biological liquids. The letter, addressed to its Tarrytown, New York office dated May 29, said the company violated good manufacturing practices over changes made to its AD VIA Centaur iPTH immunoassay. The regulator faulted the company on alleged procedural violations to ensure the design fit the requirements for the device’s intended use. The company was missing documents to demonstrate that formal documented reviews of the design were being conducted at the appropriate stages.